Not sure why but this link doesn't open for me. I found the same article on the regular kotaku.com page here: https://kotaku.com/rare-pokemon-game-worth-yellow-wata-games....
In any case, later on in the article it discusses that the buyer and seller are "working through the dispute process with PayPal, which is currently ongoing". Considering the value of the cartridge, did the buyer not opt to buy insurance on the shipment? Does PayPal offer insurance on purchases? For something such high value, not purchasing insurance seems like a disaster waiting to happen.